Make Closure Trusted Types integration not require TrustedURL values,…

… as they will soon be removed from the Trusted Types API - w3c/trusted-types#204.

goog.createTrustedTypesPolicy will attempt to create a default policy allowing any value to be converted to TrustedURL.

RELNOTES: Trusted Types integrations will allow any value to be a TrustedURL via defensively creating a 'default' policy (to prepare for TrustedURL deprecation)

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=264626714

closure/goog/base.js

@@ -4168,6 +4168,21 @@ goog.createTrustedTypesPolicy = function(name) {
   } catch (e) {
     goog.logToConsole_(e.message);
   }
+
+  // TrustedTypes API will deprecate TrustedURLs in Chrome 78. To prepare for
+  // that, and make the Closure code emulate the post-deprecation behavior
+  // of the API, we attempt to create a default policy that blesses any value
+  // to TrustedURL. This is a best-effort attempt. If that does not succeed,
+  // the application fails close - TrustedURL values will simply be required
+  // at all relevant sinks.
+  if (typeof TrustedURL !== 'undefined' && TrustedTypes.getPolicyNames &&
+      TrustedTypes.getPolicyNames().indexOf('default') === -1) {
+    try {
+      TrustedTypes.createPolicy('default', {createURL: goog.identity_}, true);
+    } catch (e) {
+      goog.logToConsole_(e.message);
+    }
+  }
   return policy;
 };